When multi-core optical fibers are connected by optical connectors, it is necessary to align the cores of the optical fibers. For alignment, there are a method of adjusting a position in the horizontal and vertical directions in the cross-section of the optical fiber and a method of adjusting a rotation angle where a center axis corresponds to the longitudinal direction of the optical fiber (see, for example, Non-Patent Document 1).
In a multi-fiber optical connector that connects a plurality of multi-core optical fibers collectively, a method using individual blocks has been proposed as a method of adjusting a rotation angle of a plurality of multi-core optical fibers. In such a method, a plurality of multi-core optical fibers are accommodated in individual blocks, respectively, and the rotation angle is aligned. The plurality of aligned individual blocks are arranged side by side and are accommodated in an accommodating portion in a ferrule (for example, see Patent Document 2).